energy

• a system is an object or group of objects
• energy is never created or destroyed, only transferred from one form to another
• energy stores:

  • thermal energy
  • kinetic energy
  • gravitational potential energy
  • elastic energy
  • magnetic energy
  • electrostatic
  • chemical energy
  • nuclear energy
• when a system is changed by:

  • heating

  • work done by forces

  • work done when a current flows
• energy stores are transferred by:

  • mechanically
  • heating
  • electrically
  • radiation
  • light
  • sound
• system is where energy is transferred
• open system: can gain or lose energy to the outside world
• as an object falls, energy is transferred from its gravitational energy store to its kinetic energy store
• closed system: no matter nor energy can enter or leave
• work done= force x distance
• mechanical uses a force to move an object
• electrical- when current flows energy is required to overcome the resistance in a circuit
• kinetic energy: energy of an object that is in motion, measured in joules (J)
• kinetic energy = 1/2 x mass (kg) x speed squared (m/s) (m x v squared)
• elastic potential energy = 0.5 x spring constant x extension squared
• gravitational potential energy: energy stored in an object due to its position above the ground
• gravitational potential energy = mass (kg)x gravitational field strength ( N/kg) x height (kg)
• earths gravitational potential field strength is 9.8 N/kg
• weight: the force of gravity acting on an object, measured in newtons (N)
• mass: the amount of matter in an object, measured in kilograms (kg)
• weight = mass x gravitational field strength
• the mass of an object is the same everywhere in the universe
• specific heat capacity is the amount of energy needed to raise the temperature of 1kg of a substance by 1 degree
• change of thermal energy = mass (kg) x specific heat capacity (J/kg degrees) x temperature change (degrees)
• power: the rate at which energy is transferred or the rate at which work is done.
• power (w) = energy transferred ( J)/ time (s)
• Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed.
• reducing unwanted energy transfer:

  • sealed closed - air isn't able to pass out (would lose heat energy by convection)
  • Double-glazed windows ( reduces conduction )
  • thick walls ( low thermal conductivity )
  • cavity walls with insulating foam (air gap reduces conduction because air is a really poor conductor )
• The higher the thermal conductivity of a material the higher the rate of energy transfer by conduction across the material.
• lubrication reduces the friction between surfaces, which reduces the amount of energy needed to move the object
• efficiency : proportion of useful energy supplied
• efficiency = useful energy transfer / total input energy transfer
• efficiency = useful power output / total power input
• increase the efficiency by using:

  • thermal insulation
  • lubrication
  • streamlining
• The main energy resources available for use on Earth include:

  • fossil fuels (coal, oil and gas),
  • nuclear fuel,
  • bio-fuel,
  • wind,
  • hydroelectricity,
  • geothermal,
  • the tides,
  • the Sun and water waves.
• A renewable energy resource is one that is being (or can be) replenished as it is used.
• The uses of energy resources include:

  • transport,
  • electricity generation
  • and heating.
• renewable energy:

  • bio-fuel
  • wind
  • hydro-electricity
  • geothermal
  • the tides
  • sun
  • water waves
• non-renewable energy:

  • fossil fuels ( coal, oil and gas)
  • nuclear fuel